Device for recovering energy

ABSTRACT

A device for recovering energy in working machines, with at least one power drive, which can be actuated to move a load mass back and forth, and with an energy storage system ( 16 ) which absorbs the energy released in the movement of the load mass in one direction and which makes it available for a subsequent movement in the other direction, is characterized in that there is an energy storage system in the form of an accumulator cylinder ( 16 ) which, mechanically coupled to the load mass, stores pneumatic pressure energy for movement in one direction, and, for movement in the other direction, acts as an auxiliary working cylinder which supports the power drive and which converts the stored pressure energy into driving force.

The invention relates to a device for recovering energy in workingmachines, with at least one power drive, which can be actuated to move aload mass back and forth, and with an energy storage system, whichabsorbs the energy released in the movement of the load mass in onedirection and which makes it available for a subsequent movement in theother direction.

Devices of this type for recovery of potential energy in workingmachines are prior art; see, for example, WO 93/11363 or EP 0 789 816B1. As energy storage systems, such devices have pressure accumulatorswhich store the released potential energy as pressure energy of aworking gas. It is crucial for the efficiency of these devices that thelowest possible energy losses occur in operation. Said losses consistprimarily of losses of thermal energy of the accumulator gas. Generally,a large part of the thermal energy which forms when the working gas iscompressed is released via the outer walls of the hydraulic accumulatorwhich is used in the prior art as an energy storage system, and thelarge-area contact region between the working gas and the exterior canlead to considerable heat losses for the relatively large surface of theaccumulator housing (preferably of steel) under consideration.

In light of these problems, the object of the invention is to provide adevice of the type under consideration which, in contrast, ischaracterized by a greatly improved energy balance with an especiallysimple and money-saving design.

According to the invention, this object is achieved by a device whichhas the features of claim 1 in its entirety.

Accordingly, an important particularity of the invention consists inthat there is an energy storage system in the form of an accumulatorcylinder which, mechanically coupled to the load mass, stores pneumaticpressure energy for movement in one direction, and for movement in theother direction acts as an auxiliary working cylinder which supports thepower drive and which converts the stored pressure energy into drivingforce.

In one especially preferred embodiment, it is stipulated that theaccumulator cylinder as the auxiliary working cylinder is coupled to aload mass which is to be raised and lowered and stores potential energyreleased in lowering processes in the form of pneumatic pressure energy.

The use of an energy storage system in the form of an accumulatorcylinder as a replacement of conventional hydraulic accumulatorsimproves the energy balance in more than one respect. On the one hand,the direct mechanical coupling of the accumulator cylinder to the loadmass, as a result of which the stored pressure energy can be converteddirectly into lifting force so that the accumulator cylinder acts as anadditional power drive, results in the elimination of the hydraulicsystem as required in the prior art between the hydraulic accumulatorand power drive, so that the associated energy losses, which otherwiseoccur, are eliminated. Furthermore, an accumulator cylinder, whencompared to a hydraulic accumulator, affords considerably more designoptions for reducing the direct heat loss of the working gas.

This direct heat loss can be reduced quite significantly when, forespecially advantageous exemplary embodiments, the piston rod of theaccumulator cylinder that exhibits a hollow, end-side open part formsthe piston whose cavity in the position fully retracted into thecylinder contains essentially the entire volume of the working gas. Inthis construction of the piston, generation of heat takes place when thepiston rod is lowered within the piston, that is, in a region which isisolated from the cylinder wall by the wall of the hollow piston. Since,moreover, the piston is dimensioned such that in its cavity it containsessentially the entire volume of the working gas; when the piston isfully retracted, in this operating state which corresponds to thestrongest compression and, thus, to the greatest generation of heat, thepiston wall extends over the entire length of the cylinder so that it isdouble walled in this state of greatest generation of heat. Heat loss isthus minimized.

On the other hand, in this construction, as a result of the specificoverall length of the piston, in the fully extended position its wallwith a corresponding flat portion is outside the cylinder wall. In thisfully extended position, the working gas has cooled in response to theexpansion. At the same time, for this piston position the wall surfacewhich is exposed to the exterior, formed from a cylinder surface and theexposed jacket surface of the piston, has a maximum value. Accordingly,the thermal resistance of the total wall area is minimal so that arelatively large amount of thermal energy is absorbed from the ambientair and released to the cooled working gas. This results in an optimalenergy balance.

Not only does the double wall arrangement which is present in certainsections contribute to optimization of the thermal energy balance, butalso the working or operating medium enclosed in the double wall, forexample, in the form of a working gas and/or in the form of hydraulicoil.

The accumulator cylinder can be formed in the shape of a cup on whoseclosed bottom there is a filler port for the working gas, such as N₂.

In especially advantageous exemplary embodiments, on the open end of theaccumulator cylinder, opposite the bottom, a guide is formed whichguides the outside of the piston at a distance from the inner wall ofthe cup, which distance forms an oil gap.

Preferably, on the open end of the piston, a second guide is formedwhich guides the end of the piston while maintaining the oil gap. Inthis way, the piston can be guided without problems.

In particular, together with an oil charge located in the oil gap, ahigh pressure sealing system can be formed which works reliably inlong-term operation even in applications with high pressures, forexample, of more than 100 bar.

In order to accommodate the oil that is displaced when the piston isextended and with the resulting reduction of the length of the oil gapand to make it available again upon retraction, a hydraulic accumulatorcan be connected to the oil gap; said accumulator compensates forchanges of the volume of the oil gap when the piston moves.

In especially advantageous exemplary embodiments, the accumulatorcylinder is used as an auxiliary working cylinder which is mechanicallyshunted to a hydraulic working cylinder which can be actuated by thehydraulic system and which is used as a power drive. This enables anespecially simple construction, especially for hoists, crane booms, andthe like, where hydraulic cylinders are provided as a power drive whichacts directly on the load mass.

While in the prior art recovered energy is available in the form ofhydraulic pressure energy from a hydraulic accumulator, so that therecovered energy can be used only for hydraulic power drives such asworking cylinders or hydraulic motors, the invention can be used inconjunction with any power drives which need not be able to behydraulically actuated, for example, in spindle drives, cable pulls, orthe like, which are activated by an electric motor and which areprovided for the lifting of loads.

The invention is detailed below using the exemplary embodiments shown inthe drawings.

FIG. 1 shows a schematically simplified representation of a crane boom,provided with one exemplary embodiment of the device according to theinvention for recovering potential energy;

FIG. 2 shows a symbolic representation which shows an accumulatorcylinder in mechanical shunting to a working cylinder in explanation ofthe operating principle of the invention;

FIG. 3 shows a schematically simplified longitudinal section of anaccumulator cylinder of a first exemplary embodiment of the deviceaccording to the invention;

FIG. 4 shows a longitudinal section of a second exemplary embodimentcorresponding to FIG. 3, and

FIGS. 5 and 6 show corresponding sections of a third and a fourthexemplary embodiment of the device.

The invention is explained below using exemplary embodiments in which acrane boom 2 forms a load mass 4 (FIG. 2). The boom 2 can be raised bymeans of a power drive in the form of a hydraulic working cylinder 6;more specifically, it can be pivoted around a coupling point 8. Theworking cylinder 6 is a hydraulic cylinder which can be actuated by ahydraulic system 10, which is symbolically represented only in FIG. 2,of which only a control valve arrangement is numbered 12 and a hydraulicpump is designated as 14; see FIG. 2. The hydraulic system 10 can be, inparticular, of a design that is conventional for working machines, sothat it need not be detailed here.

An accumulator cylinder 16 is mechanically shunted to the workingcylinder 6 which forms the power drive; i.e., the piston rod 18 of theaccumulator cylinder 16, like the piston rod 20 of the working cylinder6, acts directly on the load mass 4 (boom 2).

FIG. 3, in a separate representation, shows details of the accumulatorcylinder 16. As is apparent, it has the shape of a cup 22 with a closedbottom 24, on the latter there being a filler port, which is not shownin the figure, for a working gas, in this example N₂. In the illustratedexample, the end of the piston rod 18 forms the piston 26 in the form ofa hollow body with an inner cavity 30 which is open on the piston end 28and which in the fully retracted position of the piston 26, when thepiston end 28 is on the bottom 24 of the cup 22, contains the entirevolume of working gas. FIG. 3 shows the piston 26 more or less in themiddle position in which the gas volume is composed of the inner spaceof the cup 22 free of the piston 26 and the cavity 30 of the piston 26.

The piston 26 is guided on the inner wall of the cup 22 of theaccumulator cylinder 16 such that there is an oil gap 32 on the outsideof the piston 26. For this purpose, there is a guide 36 for the piston26 on the open end 34 of the cup 22. On the open piston end 28, there isa second guide 38. Both guides 36, 38 ensure preservation of the oil gap32 during piston movements, and they are additionally each provided witha seal arrangement 40 so that together with oil filling of the oil gap32 not only piston lubrication, but also a high pressure sealing systemare formed. In order to compensate for the volume of the oil gap 32,which varies during piston movements, a hydraulic accumulator 42 isconnected to the oil gap 32 and accommodates the oil displaced when thepiston 26 is extended and releases it again when the piston 26 isretracted.

As mentioned, in FIG. 3 the piston 26 is in a middle position at whichthe load mass 4 is partially lowered. If the load mass 4 is completelylowered, the piston 26 moves in the direction of the bottom 24 of thecup 22 so that the piston end 28 in the end position of the loweringmotion approaches the bottom 24. When the piston 26 is retracted, theworking gas is compressed to a volume which corresponds to the volume ofthe cavity 30 of the piston 26 in the fully retracted position. In thisway, the potential energy of the load mass 4 that is released duringlowering is converted into pressure energy in the accumulator cylinder16. The fully retracted position of the piston 26 corresponds to thestate of strongest compression and thus to the maximum heating of theworking gas. At the same time, in the invention in this operating state,the heated working gas is enclosed double walled, because the pistonwall 44 in this position extends over the entire length of the cup 22along the cup wall 46. In addition, the medium which has collected inthe oil gap 32 and which extends essentially over the entire length ofthe cup 22 forms an additional insulating layer between the cup wall 46and piston wall 44.

In the state of maximum heating, the accumulator cylinder 26 is thus atthe same time in the state of best heat insulation. On the other hand,in the fully extended position of the piston 26, that is, a state inwhich as a result of expansion the working gas is in the most heavilycooled state, the piston 26 with almost the entire length of its pistonwall 44 is outside the cup 22; i.e., during the “supercooled” operatingstate, the accumulator cylinder 16 exhibits the highest value of thewall surface which is exposed to the exterior, specifically, theessentially entire surface of the cup wall 46 and the piston wall 44, sothat a relatively large amount of heat can be absorbed from the ambientair. Therefore, the energy balance is good overall due to the low heatrelease for the “superheated” state and the high heat absorption for the“supercooled” state of the working gas in the invention.

FIG. 4 shows one exemplary embodiment which is simplified compared toFIG. 3 to the extent that there is no hydraulic accumulator at the oilgap 32. Instead, the oil gap 32 does not contain a complete oil charge,but is divided into an oil side 62 which contains an oil charge and agas side 64 which is filled with nitrogen by a floating, that is,axially movable seal 60. In the movements of the piston 26, the oil gapthus forms a type of miniaturized hydraulic accumulator.

FIG. 5 shows a further modified example, in which, with the hydraulicaccumulator 42 connected to the oil gap 32, the accumulator's gas sideis connected to the interior of the piston 26 via a charging line 66 sothat the filling pressure of the accumulator 42 is automatically held atthe pressure level of the working cylinder 16. There can be pressurelimitation and/or check valves in the charging line 66, which is notshown, in order to dictate the filling pressure of the hydraulicaccumulator 42 or guide it in one direction, if so desired. In amodification of this solution, it can also be advantageous to connectthe line 66 to the bottom 24 of the accumulator cylinder 16 and not inthe region of the upper, head-side cover of the piston rod 18 so thatthere is a direct fluid-carrying connection between the interior of theworking cylinder 16 and the accumulator 42, specifically, on the side ofthe accumulator 42 which is opposite the outlet site of the line whichleads to the space 32.

FIG. 6 shows another version in which the interior of the accumulatorcylinder 6 is connected to a supply source 70 for working gas via asupply line 68. Moreover, to further improve heat insulation, the innercavity 30 of the piston 26 is completely filled with a large-pore foammaterial 72 which can partially also accommodate the working gas.

It should be noted that in the highly schematically simplifiedrepresentations of FIGS. 3 to 6, which illustrate only the operatingprinciple, design details have been omitted, for example, a dividedconfiguration of the open end 34 of the cup 22 which enablesinstallation of the piston 26 or connections for delivery of the mediainto the oil gap 32.

1. A device for recovering energy in working machines, with at least onepower drive (6), which can be actuated to move a load mass (4) back andforth, and with an energy storage system (16), which absorbs the energyreleased in the movement of the load mass (4) in one direction and whichmakes it available for a subsequent movement in the other direction,characterized in that there is an energy storage system in the form ofan accumulator cylinder (16) which, mechanically coupled to the loadmass (4), stores pneumatic pressure energy for movement in onedirection, and, for movement in the other direction, acts as anauxiliary working cylinder which supports the power drive (6) and whichconverts the stored pressure energy into driving force.
 2. The deviceaccording to claim 1, characterized in that the accumulator cylinder(16) as the auxiliary working cylinder is coupled to a load mass (4)which can be raised and lowered and stores potential energy released inlowering processes in the form of pneumatic pressure energy.
 3. Thedevice according to claim 1 or 2, characterized in that the piston rod(18) of the accumulator cylinder (16) with a hollow, end-side open partforms the piston (26) whose cavity (30) in the position fully retractedinto the cylinder (16) contains essentially the entire volume of theworking gas.
 4. The device according to claim 1 characterized in thatthe accumulator cylinder (16) has the shape of a cup (22) on whoseclosed bottom (24) there is a filler port for the working gas, such asN2.
 5. The device according to claim 3, characterized in that on theopen end (34) of the accumulator cylinder (16) a guide (36) is formedwhich guides the outside of the piston (26) at a distance from the innerwall (46) of the cup (22), which distance forms an oil gap (32).
 6. Thedevice according to claim 1, characterized in that on the open end (28)of the piston (26) a second guide (38) is formed which guides the end(28) of the piston (26) while maintaining the oil gap (32).
 7. Thedevice according to claim 1, characterized in that the two guides (36,38), together with an oil charge located in the oil gap (32), form ahigh pressure sealing system.
 8. The device according to claim 1,characterized in that a hydraulic accumulator (42) is connected to theoil gap (32) and compensates for changes of the volume of the oil chargein the oil gap (32) when the piston (26) moves.
 9. The device accordingto claim 1, characterized in that the accumulator cylinder (16), as anauxiliary working cylinder, is mechanically shunted to a hydraulicworking cylinder (6) which can be actuated by a hydraulic system (10)and which is used as a power drive.